Modulated air surface particle detector

ABSTRACT

A device for counting particles on a sample surface includes a scanner probe having a first opening for receiving particles from a sample surface and one or more second openings, a particle detector for detecting particles passed there-through, a modulator for modulating air flowing there-through, a pump for producing a first airstream flowing from the first opening and through the particle detector, and for producing a second airstream flowing through the modulator and to the one or more second openings, and control circuitry for controlling the modulator to modulate an amplitude of the second airstream.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/454,649, filed Feb. 3, 2017, and which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to particle counting for cleanroom applications, and relates more particularly to an improved devicefor moving particles off of a surface and into a particle counter forthe purpose of ascertaining contamination levels.

BACKGROUND OF THE INVENTION

Contamination detection and quantification requirements have becomeincreasingly important, particularly with the rapid evolution ofhigh-tech industries. For example, the semiconductor industry hasdeveloped technology for precisely producing microelectronic devices. Inorder to reliably produce such products, highly stringent contaminationstandards must be maintained in the production facilities.

In an effort to control and minimize contamination in crucial stages ofa production process, “cleanrooms” are frequently used. A cleanroom is aroom in which the air filtration, air distribution, utilities, materialsof construction, equipment, and operating procedures are specified andregulated to control airborne particle concentrations to meetappropriate airborne particulate cleanliness classifications.

It is important to monitor the cleanliness/contamination levels in acleanroom, especially for detecting particles on a cleanroom surface.Visual inspection techniques have been used with ultraviolet or obliquewhite light. Ultraviolet light is employed to take advantage of the factthat certain organic particles fluoresce. Alternatively, white light isshined towards the test surface at an angle so as to produce reflectionsthat can be visualized. While the white light technique is slightly moresensitive than the ultraviolet technique, they both suffer from the samelimitations. These visual inspection techniques only allow a cursoryinspection of the surface conditions. They do not provide quantitativedata. Also, the visual inspection techniques, at best, only detectparticles that are larger than twenty microns. It is often desirable todetect particles that are less than one micron.

Another inspection technique involves removing particles from a testsurface, by for example, applying a piece of adhesive tape to the testsurface. The particles on the tape are then manually quantified byputting the tape under a microscope and visually counting the particles.This technique allows the detection of particles of approximately fivemicrons or larger. The primary disadvantage of this technique is that itis very time consuming, and that it is highly sensitive to variabilitybetween operators.

A third inspection technique is disclosed in U.S. Pat. No. 5,253,538.The '538 patent discloses a device that includes a scanner probe havingat least one opening for receiving particles from the sample surface.The scanner probe is connected to a tube having first and second ends.The first end of the tube is connected to the scanner probe and thesecond end of the tube is connected to a particle counter that employsoptical laser technology. The particle counter includes a vacuumgenerator that causes air to flow from the sample surface through thescanner probe, through the tube and into the particle counter, whereparticles contained in the air stream are counted. The '538 patentdiscloses an inspection method that involves the use of the particlecounting device. A background particle level of zero is firstestablished by holding the scanner probe near the cleanroom supply airand taking repeated readings, or by installing an optional zero-countfilter in the particle counter. Next, the hand-held scanner probe ispassed over the sample surface at a constant rate for a predeterminedtest period. The test cycle is started by pushing the run switch, whichis located on the scanner probe. The particle counter counts and readsout a number corresponding to the average number of particles per unitarea. The process is usually repeated several times along adjacentsurface areas, each time yielding a “test reading”.

An improvement of the technique disclosed in the '538 patent is onedisclosed in U.S. Pat. No. 7,010,991, which is incorporated herein byreference for all purposes. The '991 patent describes a device forcounting particles on a sample surface. The device includes a scannerprobe having at least one opening for receiving particles from a samplesurface, a particle counter for counting particles passed there-through,a conduit having a first end connected to the scanner probe and a secondend connected to the particle counter, wherein the conduit includesfirst and second tubes, a sensor and a controller. The particle counterincludes a pump for producing an airstream flowing from the scannerprobe opening, through the first tube, through the particle counter, andback to the scanner probe via the second tube, for carrying theparticles to the particle counter for quantitation and delivering anairstream flowing back to the scanner probe. The sensor measures a rateof flow of the airstream. The controller controls a speed of the pump inresponse to the measured rate of flow of the airstream to maintain theairstream at a constant flow rate while the particle counter quantitatesthe particles in the airstream.

The '991 patent further describes a device including a scanner probehaving at least one opening for receiving particles from a samplesurface, a conduit having a first end connected to the scanner probe anda second end terminating in a first connector, wherein the conduitincludes first and second tubes; a particle counter, electronic indicia,and a controller. The particle counter counts particles passedthere-through, and includes a port for receiving the first connector anda pump for producing an airstream flowing from the scanner probeopening, through the first tube, through the particle counter, and backto the scanner probe via the second tube, for carrying the particles tothe particle counter for quantitation and delivering an airstreamflowing back to the scanner probe. The electronic indicia is disposed inat least one of the first connector, the conduit and the scanner probefor identifying at least one characteristic of the scanner probe. Thecontroller detects the electronic indicia via the port and firstconnector, and controls the particle counter in response to the detectedelectronic indicia.

The '991 patent further describes a device including a scanner probehaving at least one opening for receiving particles from a samplesurface, a particle counter for analyzing particles passedthere-through, and a conduit having a first end connected to the scannerprobe and a second end connected to the particle counter. The conduitincludes first and second tubes. The particle counter includes a pumpfor producing an airstream flowing from the scanner probe opening,through the first tube, through the particle counter, and back to thescanner probe via the second tube, for carrying the particles to theparticle counter and delivering an airstream flowing back to the scannerprobe. The particle counter also includes a particle detector forcounting the particles in the airstream coming from the scanner probe, afilter cartridge port through which the airstream flows after passingthrough the particle detector, and a filter cartridge removablyconnected to the filter cartridge port for capturing the particles inthe airstream after being counted by the particle detector.

The efficiency of the above described particle counting devices can beclassified as the number of particles extracted from the sample surfaceand captured/counted by the device, divided by the total number ofparticles on the sample surface. In order for a particle to beextracted, the air flow across the sample surface created by the scannerprobe must be sufficient to overcome the adhesion force between theparticle and the sample surface. One known problem of conventionalscanner probes, however, is that as the airflow rate of the airstream isincreased to attempt to better overcome the adhesion forces of moreparticles, more of the dislodged particles can be blown away from thescanner probe in which case they are never captured and counted by thedevice. This problem is called particle ejection, where particlesdislodged by the scanner probe are ejected from the area under thescanner probe, where the particles cannot be captured and detected.Thus, merely increasing the velocity of airstream into the scanner probecan result in lower efficiency due to particle ejection, and thereforescanner probe efficiency cannot be fully maximized simply by increasingthe velocity of the airstream. Because of particle ejection, there is alimit to the efficiency of these devices.

BRIEF SUMMARY OF THE INVENTION

The aforementioned problems and needs are addressed by a device forcounting particles on a sample surface that includes a scanner probehaving a first opening for receiving particles from a sample surface andone or more second openings, a particle detector for detecting particlespassed there-through, a modulator for modulating air flowingthere-through, a pump for producing a first airstream flowing from thefirst opening and through the particle detector, and for producing asecond airstream flowing through the modulator and to the one or moresecond openings, and control circuitry for controlling the modulator tomodulate an amplitude of the second airstream.

A device for counting particles on a sample surface includes a scannerprobe having a first opening for receiving particles from a samplesurface and one or more second openings, a particle detector fordetecting particles passed there-through, a modulator for modulating airflowing there-through, a pump for producing a first airstream flowingfrom the first opening and through the particle detector and through themodulator, and for producing a second airstream flowing to the one ormore second openings, and control circuitry for controlling themodulator to modulate an amplitude of the first airstream.

Other objects and features of the present invention will become apparentby a review of the specification, claims and appended figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the particle counter assembly.

FIG. 2A is a top perspective view of the scanner probe.

FIG. 2B is a bottom perspective view of the scanner probe.

FIG. 3A is a side cross sectional view of the scanner probe and testingsurface before particle detection.

FIG. 3B is a side cross sectional view of the scanner probe and testingsurface after particle detection using unmodulated air flow.

FIG. 4A is a side cross sectional view of the scanner probe and testingsurface before particle detection.

FIG. 4B is a side cross sectional view of the scanner probe and testingsurface after particle detection using modulated air flow.

FIG. 5 is a block schematic diagram of the particle counter assembly andthe scanner probe.

FIG. 6 is a block schematic diagram of the particle counter assembly andthe scanner probe.

FIG. 7 is a timing diagram for the operation of the particle detector.

FIG. 8 is a block schematic diagram of the particle counter assembly andthe scanner probe.

FIG. 9 is a block schematic diagram of the particle counter assembly andthe scanner probe.

FIG. 10 is a block schematic diagram of the particle counter assemblyand the scanner probe.

FIG. 11 is a block schematic diagram of the particle counter assemblyand the scanner probe.

FIG. 12 is an illustration of the user interface screen of the particledetector.

FIG. 13 is a block schematic diagram of the particle counter assemblyand the scanner probe.

FIG. 14 is a block schematic diagram of the particle counter assemblyand the scanner probe.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an improvement over the previously describedscanner probe devices. It has been discovered by the present inventorsthat modulating the air flow rate into the scanner probe results ingreater peak air velocities across the tested surface to dislodge moreof the particles, yet also results in less particles that are lost bybeing blow out of and away from the scanner probe (i.e. lower particleejection). It has also been discovered that the frequency of the airflow modulation affects the efficiency of the system. The frequency ispreferably selected to maximize surface shear for particle displacement,to avoid (preferably exceed) the natural resonant frequency of scannerprobe face to avoid particle generation by the scanner probe face, andto maximize particle dislodgement off the probed surface (also called“re-suspension”) by resonating the particles off of the surface (i.e.,use an air flow frequency near or at the natural frequency of theparticle). The modulated airstream has been found to effectively rock orstimulate particles off of rough surfaces.

The present invention improves Particle Efficiency PE (which is equal tothe particles picked up and delivered to the detector divided by thetotal particles at the beginning of the test on the surface under thescanner probe head). For example if there are 10 particles on thesurface under the scanner probe, and normally 6 particles are picked upand transported in the vacuum line to the detector using a constant flowrate, then the Particle Efficiency PE is 60%. With the modulated airsurface particle detector, with the 10 particles under the probe head,particle ejection is minimized, meaning that an additional particle iscaptured instead of being ejected, and two more additional particles aredislodged and captured instead of staying on the probed surface,Particle Efficiency PE is increased to 9 out of 10 particles, or 90%.Modulating the air flow achieves both decreased ejection and increasedenergy to break the adhesion force for certain particles that would notovercome their adhesion force with constant air flow. The increasedenergy is accomplished through increasing air shear that can increaseaerodynamic drag, which excites the particle to move by vibrating theparticle close to its resonance frequency, and/or increasing theturbulence of the air flow over the particle to increase the changes ofresuspension. Thus, Particle Efficiency is improved by modulating theair flowing to the scanner probe, and thus across the scanner probehead, to resonate or disturb the particles and overcome the adhesionforce of the particle on the surface so it can be removed.

FIG. 1 shows the primary components of the particle detector 1 foranalyzing particles on a sample surface. The main detector componentsinclude a particle counter assembly 8, a scanner probe 10, and conduit22 connected between the particle counter assembly 8 and probe 10.

FIGS. 2A and 2B illustrate the scanner probe 10, which includes asubstantially planar base 12. The scanner base 12 has a bottom side 14for interfacing with the sample surface. The scanner base 12 isperpendicularly connected to a scanner handle 16 which includes acontrol section 18 having run switch 20 for activating the particledetector and an LED light 48 indicating that particle counting is inprogress. The conduit 22 includes a pair of tubes 24 and 26 (supply andreturn hoses, respectively) each having a first and a second end. Thefirst ends of the tubes 24/26 are connected to the scanner handle 16,and the second ends are connected to a port or connector in the particlecounter assembly 8. The conduit 22 also includes electrical wiring 28which electrically connects the scanner probe 10 to the particle counterassembly 8.

The base portion 12 of the scanner probe 10 has two coin-shaped portions30 and 32 which are fastened together by screws 34. The scannerembodiment shown in FIGS. 2A and 2B is designed primarily for picking upparticles off of a substantially flat surface. However, scanners ofother shapes which are specifically designed to conform to non-flatsample surfaces could also be used. Coin-shaped portion 30 of thescanner base 12 is also referred to as a face plate, and is preferablymade of a material which is impregnated with a friction limitingnon-particulating substance, for example, hard black anodized aluminumwith Teflon impregnation, type 3, class 2, mil spec A8625D. The scannerhandle 16 has two bores 36 and 38 for receiving the supply and returntubes 24/26. Another hole 40 is provided in the handle 16 for receivingthe electrical wiring 28 from the conduit 22.

The scanner base bottom side 14 is designed to interface with the samplesurface. In this embodiment, the bottom side 14 has a hole 42 (i.e., afirst opening) which is located approximately in the center of the baseplate bottom side 14. The hole 42 is connected to the bore 36 in thescanner handle 16 which is connected to the return tube 26 of conduit22. Particles from the sample surface are sucked through the face platehole 42 for the purpose of counting the particles in the particlecounter assembly 8. The base plate bottom side 14 also has a pluralityof smaller holes 44 (i.e., second openings) which converge into thescanner handle bore 38, which is connected to the air supply tube 24 ofconduit 22. Air is supplied from the particle counter assembly 8 anddelivered through the face plate holes 44 onto the sample surface fordislodging and fluidizing particles so that they may be sucked throughface plate hole 42 for counting. Face plate bottom side 14 also hasintersecting grooves 46 for channeling dislodged particles into faceplate hole 42.

FIGS. 3A-3B and 4A-4B illustrate the increased Particle Efficiency ofthe modulated air system versus a constant amplitude air system of theparticle detector 1. FIG. 3A illustrates ten particles 50 disposed underthe scanner probe 10 on a surface 52 to be tested. FIG. 3B illustratesthe state of the surface 52 after the use of constant air flow suppliedto the scanner probe 10 to extract and detect the particles. Of theoriginal ten particles, two particles remain under the scanner probe 10as un-extracted particles, and two particles are dislodged from the areaunder the scanner probe 10 as ejected particles. Therefore, of the tenoriginal particles, six were successfully extracted into the scannerprobe and sent to the particle counter assembly 8 for counting. Countingsix of the ten particles provides a particle efficiency PE of 60%.

FIG. 4A illustrates the same ten particles 50 disposed under the scannerprobe 10 on a surface 52 to be tested. FIG. 4B illustrates the state ofthe surface 52 after the use of a modulated air flow supplied to thescanner probe 10 to extract and detect the particles. Of the originalten particles, only one particle remains under the scanner probe 10 asan un-extracted particle, and no particles are dislodged from the areaunder the scanner probe 10 as ejected particles. Therefore, of the tenoriginal particles, nine were successfully extracted into the scannerprobe and sent to the particle counter assembly 8 for counting. Countingnine of the ten particles provides a particle efficiency PE of 90%.

The modulated air flow to increase turbulence and/or air sheer acting onthe particles can be provided in different ways. For example, air can bepumped into a temporary air tank and released to increase peak air flowand overcome the adhesion force of the particle on the surface so it canbe removed. The air supply line to the scanner probe can be periodicallyshut off so only the vacuum line is drawing in the particles and avoidsblowing the particles from under the probe. A piezo electric modulatorin the system or in the probe face or in the air supply line of thescanner probe can be used to modulate the air flow. The modulationfrequency is preferably set to avoid probe resonance and harmonics sothe scanner probe 10 does not vibrate on the surface. Scanner probeoscillations can be dampened with a gasket or O-ring disposed betweenthe probe 10 and surface under test. The pump can be turned on and offto modulate the air flow. A tank (i.e., gas reservoir) can be used tobuild up pressure and/or vacuum during the test or between tests, andthen be used to release the pressure to increase air shear andmodulation. A valve can be used to modulate the air to increase airshear and modulation.

To enhance particle extraction, the modulation frequency can be sweptacross a range of frequencies (e.g., from some low frequency to a higherfrequency), and/or can be changed among several discrete frequencies, toaddress different particle sizes and materials that may be present onthe test surface (i.e., for dislodging different types of particleshaving different resonant frequencies and/or adhesion forces). Theparticle counter assembly 8 additionally can include an in-line dryer ordesiccant dryer to remove moisture from the air being supplied to thescanner probe 10, which can decrease the adhesion force between theparticle and the surface arising from surface tension. Preferably, theconnection between the particle counter assembly 8 and the scanner probe10 conveys to the particle counter assembly 8 information about whichtype of scanner probe 10 is attached so the control circuitry and/orsoftware of the particle counter assembly 8 can know the resonancefrequency of the particular attached scanner probe 10 attached and beingused for the surface scanning.

FIG. 5 illustrates a first embodiment of the particle counter assembly 8for providing the modulated air flow. Particle counter assembly 8preferably includes a connector 54 for connecting to the conduit 22 in aremovable manner, so that different types of scanner probes 10 can beeasily connected to the particle counter assembly 8. Air lines 56 arerepresented by the arrows in FIG. 5. The airstream from the scannerprobe 8 passes through the connector 54 and to a particle detector 58,which can be any appropriate detector capable of detecting and countingparticles in an air stream. Preferably, particle detector 58 is a laserbased particle detector that is well known in the art and not furtherdescribed herein. After particles in the airstream are counted, theairstream passes through a particle filter 60 to remove particles fromthe airstream in preparation of returning to the scanner probe. Theairstream then passes through a pump 62 which creates the vacuum thatdraws the airstream from the scanner probe 10. The airstream passesthrough another filter 64 which ensures no contamination from the pumpremains in the airstream. The airstream then passes through a modulator66 that modulates the rate of flow (i.e., amplitude) of the airstream.Modulator 66 could simply be a valve or piezoelectric membrane thatmodulates the airstream headed back to the scanner probe 10. Themodulator can be configured to divert some or all of the airstream to anexhaust port 68 so that the airstream returning to the scanner probe canbe operated independently from the vacuum drawing airflow from thescanner probe 10 (i.e., the second airstream headed to the scanner probecan be operated independently from the first airstream headed to theparticle counter assembly). For example, at the beginning of theparticle counting operation, only a vacuum may be applied to the scannerprobe so that no loosely bound particles will be ejected, then later inthe particle counting operation the airstream is then applied to thescanner probe to remove particles more tightly adhered to the testsurface. The exhaust port 68 could include another air filter to preventany return contamination to the environment. Before returning to theconnector 54 and to the scanner probe 10, the airstream can pass throughan optional dryer 69 that removes moisture from the airstream todecrease the adhesive force of particles to the surface.

The control circuitry for operating the particle detector 1 can bedispersed among the components, where the various components communicatewith each other during operation so that there is coordinated operation(see FIG. 5). Alternately, there can be a central controller containingmost or all the control circuitry for controlling the operation of thevarious components in a coordinated fashion, as illustrated in FIG. 6.

FIG. 7 is a timing diagram showing the particle counting operation ofthe particle detector 1. At time=1, the user actives the run switch 20(which could be a press button), which activates the particle detector58 and activates the pump 62 to generate a vacuum that draws air fromthe scanner probe 10 and to the particle detector 58. During thisinitial time period (e.g., time=1 to time=5), the modulator 66 is notactivated to supply air back to the scanner probe 10 (i.e., there is noairstream out to the scanner probe 10, the airstream is instead divertedto the exhaust port 68). During this time, the vacuum will draw air fromthe environment and between the test surface and the bottom side 14 ofthe scanner probe, whereby this airstream will dislodge and capture lowadhesion particles that will travel with the airstream caused by thevacuum through the scanner probe 10, conduit 22 and to the particledetector 58. At a later time (e.g., time=5), the modulator 66 isactivated to modulate the amplitude of the airstream returning to thescanner probe 10 (i.e., create amplitude pulses of the airstream). Asindicated in the diagram of FIG. 7, the amplitude of the airstream goingout to the scanner probe 10 oscillates between high peak values and lowor zero values at a certain frequency. This modulated airstream resultsin modulated air velocities at the bottom side 14 of the scanner probe10 that at peak amplitude values will dislodge and capture high adhesionparticles that will travel with the airstream into scanner probe 10,through conduit 22 and to the particle detector 58. After apredetermined amount of time or number of oscillations/pulses, the pump,particle counter assembly and modulator are deactivated (e.g., attime=10), whereby the airstreams to and from the scanner probe 10ceases. It should be noted that while FIG. 7 shows only three pulses ofthe airstream going out to the scanner probe 10, there can be dozens,hundreds or more of these pulses used in a single particle countingoperation.

While the modulation frequency shown in FIG. 7 is fixed over theduration of the particle counting operation, the modulation frequencycan be varied during the particle counting operation. For example, themodulation frequency can continuously sweep over a range of modulationfrequencies during a single particle counting operation. Or, themodulation frequency can step or change between predetermined frequencymodulation values during a single particle counting operation. Or,multiple particle counting operations can be performed each using adifferent modulation frequency.

FIG. 8 illustrates an alternate embodiment of the particle counterassembly 8 for providing the modulated air flow. The modulator 66includes an air tank 72 in which air pressure builds before and betweenairstream pulses to the scanner probe 10. The pressurized air in tank 72is released by modulator 66 to create the pulses of modulated airstreamto the scanner probe 10. FIG. 9 shows the same configuration, exceptwith centralized control circuitry in the form of a central controller70.

FIG. 10 illustrates another alternate embodiment, where the airmodulator 66 is configured as part of the scanner probe 10 instead ofthe particle counter assembly 8. By locating the modulator 66 inside ofthe scanner probe 10 and close to bottom side 14 of the base 12,dampening of the air flow modulation or peak air shear that might occurbetween the particle counter assembly 8 and the scanner probe 10 can beavoided. FIG. 11 shows the same configuration, except with centralizedcontrol circuitry in the form of a central controller 70.

FIG. 12 illustrates a user interface screen 74 that can be part of theparticle counter assembly 8 or scanner probe 10, and allows the user toset the airstream amplitude, modulation frequency, modulation time, andthe delay between the start of the vacuum/detection and the beginning ofthe modulated airstream to the scanner probe 10. These parameters can beset or changed automatically upon detecting the type of scanner probethat is connected to the connector 54.

The above described operation involves modulating the amplitude of theairstream to the scanner probe 10. However, the airstream from thescanner probe 10 to the particle counter assembly 8 (caused by thevacuum from pump 62) can instead or additionally be modulated.Specifically, the air flow modulation across the scanned surface can beachieved by modulating the airstream to the scanner probe 10 and/ormodulating the airstream from the scanner probe 10. If both theairstreams to and from the scanner probe 10 are modulated, they can bemodulated in phase with each other, or out of phase with each other, tomaximize Particle Efficiency. Modulating the airstream from the scannerprobe 10 can be implemented by modulating the operation of pump 62,using the existing modulator 66 in the probe head, or including aseparate modulator 66 for the airstream from the scanner probe 10 asshown in FIGS. 13 and 14.

It is to be understood that the present invention is not limited to theembodiment(s) described above and illustrated herein, but encompassesany and all variations falling within the scope of any claims. Forexample, references to the present invention herein are not intended tolimit the scope of any claim or claim term, but instead merely makereference to one or more features that may be covered by one or moreclaims. Materials, processes and numerical examples described above areexemplary only, and should not be deemed to limit the claims. Theparticle counter assembly and the scanner probe could be combined into asingle housing, thus omitting conduit 22. A single hole 44 could be usedinstead of multiple holes 44. The two modulators 66 in FIGS. 13 and 14could be combined into a single device.

What is claimed is:
 1. A device for counting particles on a samplesurface, comprising: a scanner probe having a first opening forreceiving particles from the sample surface and one or more secondopenings; a particle detector for detecting particles passedthere-through; a modulator for modulating air flowing there-through; apump for producing a first airstream flowing from the first opening andthrough the particle detector, and for producing a second airstreamflowing through the modulator and to the one or more second openings; acontrol circuitry for controlling the modulator to modulate an amplitudeof the second airstream; and wherein the amplitude of the secondairstream is modulated as a series of pulses having a frequency thatvaries over time.
 2. The device of claim 1, wherein the amplitude of thesecond airstream is modulated as a series of pulses having a frequencythat sweeps over a range of frequencies over time.
 3. The device ofclaim 1, wherein the first and second airstreams are produced duringfirst and second time periods, and wherein the modulator blocks thesecond airstream from reaching the one or more second openings duringthe first time period and enables the second airstream to reach the oneor more second openings during the second time period which is after thefirst time period.
 4. The device of claim 1, wherein the particledetector and the pump are disposed in a particle counter assembly, andwherein the device further comprises: a conduit having a first endconnected to the scanner probe and a second end connected to theparticle counter assembly, wherein the conduit includes first and secondtubes, and wherein the first airstream flows through the first tube andthe second airstream flows through the second tube.
 5. The device ofclaim 4, wherein the modulator is disposed in the particle counterassembly.
 6. The device of claim 4, wherein the modulator is disposed inthe scanner probe.
 7. The device of claim 1, wherein the modulator andthe control circuitry are configured to modulate an amplitude of thefirst airstream.
 8. The device of claim 7, wherein the amplitude of thefirst airstream is modulated as a series of pulses having a fixedfrequency.
 9. The device of claim 7, wherein the amplitude of the firstairstream is modulated as a series of pulses having a frequency thatvaries over time.
 10. The device of claim 7, wherein the amplitude ofthe first airstream is modulated as a series of pulses having afrequency that sweeps over a range of frequencies over time.
 11. Thedevice of claim 1, wherein all of the control circuitry is disposed in acentral controller connected to the particle detector, the modulator andthe pump.
 12. The device of claim 1, further comprising: an air tank foraccumulating pressurized air, wherein the modulator is configured to usethe pressurized air to modulate the second airstream.
 13. The device ofclaim 1, further comprising: a filter for removing particles from thefirst airstream.
 14. The device of claim 1, further comprising: a filterfor removing particles from the second airstream.
 15. The device ofclaim 1, further comprising: a dryer device for removing moisture fromthe second airstream.
 16. The device of claim 1, further comprising: asecond modulator for modulating air flowing there-through, wherein thefirst airstream passes through the second modulator, and wherein thecontrol circuitry is configured to control the second modulator tomodulate an amplitude of the first airstream.
 17. A device for countingparticles on a sample surface, comprising: a scanner probe having afirst opening for receiving particles from the sample surface and one ormore second openings; a particle detector for detecting particles passedthere-through; a modulator for modulating air flowing there-through; apump for producing a first airstream flowing from the first opening andthrough the particle detector and through the modulator, and forproducing a second airstream flowing to the one or more second openings;a control circuitry for controlling the modulator to modulate anamplitude of the first airstream; a second modulator for modulating airflowing there-through, wherein the second airstream passes through thesecond modulator, and wherein the control circuitry is configured tocontrol the second modulator to modulate an amplitude of the secondairstream; and wherein the amplitude of the second airstream ismodulated as a series of pulses having a frequency that varies overtime.